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<title>fork</title>
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<h2 align=center>fork</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
fork - copy the current process
</p>

<h3>Library</h3>
<p>
Standard C Library (libc, -lc)
</p>

<h3>Synopsis</h3>
<p>
<tt>#include &lt;unistd.h&gt;</tt><br>
<br>
<tt>pid_t</tt><br>
<tt>fork(void);</tt>
</p>

<h3>Description</h3>
<p>
<tt>fork</tt> duplicates the currently running process. The two copies
are identical, except that one (the "new" one, or "child"), has a new,
unique process id, and in the other (the "parent") the process id is
unchanged.
</p>

<p>
The process id must be greater than 0.
</p>

<p>
The two processes do not share memory or open file tables; this state
is copied into the new process, and subsequent modification in one
process does not affect the other.
</p>

<p>
However, the file handle objects the file tables point to are shared,
so, for instance, calls to lseek in one process can affect the other.
</p>

<h3>Return Values</h3>
<p>
On success, <tt>fork</tt> returns twice, once in the parent process
and once in the child process. In the child process, 0 is returned. In
the parent process, the process id of the new child process is
returned.
</p>

<p>
On error, no new process is created. <tt>fork,</tt> only returns once,
returning -1, and <A HREF=errno.html>errno</A> is set according to the
error encountered.
</p>

<h3>Errors</h3>
<p>
The following error codes should be returned under the conditions
given. Other error codes may be returned for other errors not
mentioned here.

<table width=90%>
<tr><td width=5% rowspan=3>&nbsp;</td>
    <td width=10% valign=top>EMPROC</td>
				<td>The current user already has too
				many processes.</td></tr>
<tr><td valign=top>ENPROC</td>	<td>There are already too many
				processes on the system.</td></tr>
<tr><td valign=top>ENOMEM</td>	<td>Sufficient virtual memory for the new
				process was not available.</td></tr>
</table>
</p>

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